This invention relates to a unique coupling device which has proven to lend itself, in particular, to new and improved window and windshield installations. Its impact is particularly significant in the automotive industry. The invention will be therefore described in this respect, though its application is obviously not so limited and such is not intended.
The prior art has evidenced many, many problems in respect to installations involving the connection of glass or metal parts and particularly glass and metal parts. For example, with respect to the automotive industry, with past and existing practice and materials it has proven to be a difficult and arduous task to install a windshield or like structure in the provided metal frame. The difficulties have stemmed from several sources. In the first instance it has been found there must be extreme care in handling windshields, particularly in a production operation, to avoid damage. The problem in this respect has been compounded since the frames or openings for such items are usually less than precision formed. For such reasons, as well as others, the automotive companies have found there is considerable time consumed in set up and adjustment of windshields in the process of their installation. The problem is further compounded by the fact that heretofore known plastic sealing materials commonly employed for the purposes described are either so messy to handle that there is a large amount of time and money consumed in cleanup or the glass windshield must be applied in such a manner and under such pressure as to invite damage. As a matter of fact in this respect damage has proven to be quite frequent.
That in the prior art there has been no proper solution to the problems above posed is well evidenced by the fact that different automotive companies use different materials and systems for installing windshields.
For example, one Motor Company uses a cold adhesive tape to line an opening, following which a windshield is forced against the tape under the influence of a substantial hydraulic force. The object is to cold flow the tape and produce thereby a bond between the tape, the windshield and the framing structure. This has been the ultimate of the prior art as far as this Motor Company has been concerned. However, this practice has produced many cracked windshields in this Motor Company's production line. In any event, the pressures involved invariably produce residual strains in the glass structure and in many cases cracking occurs later. Moreover, technical information that has been uncovered indicates that with the prior art material and process utilized by this Motor Company the initial adhesion between the windshield and the automobile body is relatively low. This is inherent in their practice since the requirements of the adhesive tape employed dictates that the incorporated plasticizers and tackifiers be locked in to prevent sag or flow of the tape when subjected to elevated environmental temperatures, the objective being to prevent surface wetting. Where there is a maximum dimensional mismatch of body and windshield in application of the windshield, the rebound after compression is relieved causes a break in the bond line between the tape and its related structure at the point or points of minimum compression. Since initial adhesion is relatively low, in time the gap in the bond line grows, and leaks occur. Where sufficiently high pressure is used to overcome this fault, stress and cracks can readily result.
In contrast to the aforementioned procedure, another large automotive concern utilizes a relatively messy mastic material for bonding windshields rather than a cold flowed tape. This mastic resembles a soft caulking compound. In use, it is extruded and applied around the frame for a windshield in a bead form. Due to its ready flow condition it is necessary to interpose spacer blocks to contain successive sections of the mastic bead. Following the application of this bead, it must not be cured before the windshield is set in place. If the cure is too fast the mastic passes the point of usage and must be replaced. In some instances it takes much too long for the bead material to set and in such case the application and seal of the windshield is faulty. In any case, the mastic is messy on application of the windshield and it tends to flow in a manner to contaminate adjacent structural areas. This necessitates much cleaning and entails extra labor and expense in its use.
The prior art is loaded with all types of thermo-plastic and thermo-setting materials and has provided concepts of fusing, for example, thermo-plastic materials with a compatible thermo-plastic tape. Such a concept is evidenced in Wilkins U.S. Pat. No. 3,049,465. Wilkins refers to fusing like elements with a tape of similar physical characteristics. Of course, as will be self-evident, the problems are extremely different when the coupling problem has to deal with the connection of dissimilar metal and/or glass parts since here fusion is not possible in the sense of the Wilkins concept. Thus, Wilkins does not comprehend either the problems faced by the present invention or the solutions thereof as necessitated by the particular environment of the invention. As to the adhesive art, it has also been heretofore known to encase an ordinary wire in a thermo-setting resin such as revealed in U.S. Pat. No. 3,263,268 to Flaherty and to use such resin in this form to create a flow of fluid adhesive between parts. However, the disclosure of Flaherty has no more than that of Wilkins led to any improvement beneficial in the area of concern and has not achieved the benefits of the present invention. If it had, the automotive industry as well as the window industry would have jumped on the advantages afforded thereby long since. Flaherty refers to utilizing a cover portion of material such as a thermo-setting "B stage" epoxy, polyester, polyurethanes, polymerizable thermo-plastics and the like but it must be pointed out that neither the thermo-setting or thermo-plastic material of the nature noted has or can satisfactorily solve those problems to the solution of which the present invention is directed. It remains that a polymerizable thermo-plastic does in fact have the characteristics of a thermo-setting material in that it is irreversible. On application of heat, particularly in the range to be specified in accordance with the present invention, the polymerizable thermo-plastic becomes a fluid body and melts throughout. Where a wire is internally thereof the internal structure will melt first and the remainder will follow. Lacking the feature of reversibility the polymerizable material cannot be considered a true thermo-plastic. These facts are pertinent to the inability of the Flaherty material to be applied with any satisfactory result to the purposes of the present invention.
Attention is directed to the fact that nowhere in the prior art is there a disclosure of an elongate coupling strip wherein only the surface becomes fluidly adhesive upon application of a specific range of heat while the interior thereof remains essentially stable. In this aspect of the concept of an adhesive tape, well proven, already, in the automotive industry, lies a unique and unexpected result in the art of applying glass to metal and particularly in the formation of a windshield, window or like unit assembly.